JP2510704B2 - Optical fiber coupler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distributed coupling type fusion splicing type optical fiber coupler used for optical fiber communication, an optical fiber sensor, etc. The port has a non-reflective end.

[Conventional technology]

As the distributed coupling type optical fiber coupler, as shown in FIG. 3, two optical fibers 1, 1 are spliced and fused,
It is well known that a fusion-spreading type is one in which both ends 3 ...

FIG. 4 shows a wavelength division multiplexing bidirectional optical fiber communication system using such a distributed coupling type optical fiber coupler.
Reference numeral 4 in the drawing is such a distributed coupling type optical fiber coupler (hereinafter, simply referred to as a coupler). An optical fiber 5 is connected to the port A of the coupler 4, and the optical fiber 5
The transmitted light having a wavelength of 1.3 μm from the laser die auto 6 is transmitted to. An optical fiber 7 is connected to the port B, and the transmission light from the optical fiber 7 is input to the avalanche photodiode 8. Further, an optical fiber 9 is connected to the port C and serves as a main line, which has a wavelength of 1.3 from the laser diode 3.
The transmission light of μm is transmitted, and the transmission light of wavelength 1,55 μm which is transmitted in the opposite direction to this transmission light is transmitted. Then, the transmitted light having the wavelength of 1.55 μm is coupled from the port C of the coupler 4 to the port B and is sent to the avalanche photodiode 8. Further, nothing is connected to the port D, which is a connectionless end.

In such a communication system, the transmitted light with a wavelength of 1.3 μm from the laser diode 6 is almost 1 from the port A to the port C.
Although it is coupled to 00%, the isolation of coupler 4 is not infinitely large, so port A to port D
Also, for example, transmission light of about -15 to -20 dB is coupled.
If the end face of the end of port D is cut in a mirror state, the light leaked to port D is reflected here, and port D
From the optical fiber 7 to the avalanche photodiode 8, and this reflected leaked light reduces the S / N ratio of the backward transmitted light having a wavelength of 1.55 μm.

In order to solve such a problem, a method of obliquely cutting the end face of the end of the port D of the coupler 4 so that the reflected wave does not return to the coupling portion 2 again, a matching oil is applied to the end to emit light. Conventionally, a method of absorbing light and a method of coating the end with resin to absorb light have been used.

[Problems to be Solved by the Invention]

However, the method of obliquely cutting the end face of the terminal end requires time and labor for processing, and the method of applying matching oil is not suitable for long-term use due to evaporation of oil and the like. The coating method has a problem that the resin is peeled off at a low temperature and the reliability is poor.

[Means for solving the problem]

According to the present invention, the above-mentioned problem is solved by heating and extending the ends of unnecessary ports of the optical fiber coupler formed by fusion splicing with two or more optical fibers to make the ends non-reflective. I tried to solve it.

FIG. 1 shows an example of the state of termination of unnecessary ports of the coupler of the present invention. The termination of this port 11 is
The terminal of the optical fiber 12 that constitutes the coupler is partially heated by using a micro torch or the like as it is, and is stretched after being brought into a molten state, and the diameter of the optical fiber is reduced, further heated, stretched and fused. The end of the optical fiber 12 is tapered as it is. The coupler is an optical fiber coupler formed by splicing and fusing two or more optical fibers as described above. At such an end,
Since the diameter of the core of the optical fiber 12 is gradually reduced, the optical energy guided through the core leaks out from the core and is diverged as a cladding mode, resulting in an almost perfect non-reflection end.

For example, in a coupler in which two single mode optical fibers having an outer diameter of 125 μm and a core diameter of 10 μm are spliced, fused, and stretched, the unnecessary port 11 has a tapered end as shown in FIG. The return loss at port 11 was about 50 dB. In comparison with this, the return loss when the end of port 11 is simply cut off is about 14 dB.

FIG. 2 shows another example of termination of unnecessary ports of the coupler of the present invention. This example is different from the previous example in that the tapered tip is slightly curved. In this way, when the tapered tip is curved, light leakage due to bending from the core is further added, and the return loss is further increased. For example, splice two single mode optical fibers with an outer diameter of 125 μm and a core diameter of 10 μm,
In the fused and stretched coupler, the return loss exceeds the detection limit. The port 11 in this example may be formed by bending the tip portion by applying a slight external force when the optical fiber 11 is stretched or melted.

In such a coupler, since the unnecessary port 11 is heated, stretched, and fused to form a non-reflective end, the amount of reflected light becomes extremely small and the manufacturing is easy,
It is also highly durable and reliable.

〔The invention's effect〕

As described above, the optical fiber coupler of the present invention is a distributed-coupling type optical fiber coupler having two or more optical fibers and having four or more ports, and at least one of the ports is heated and drawn to reduce its diameter. Since the non-reflective end is cut by fusing, the return loss is extremely large and the non-reflective end has good characteristics. In addition, since the structure is simple, durability and reliability are high. Further, in manufacturing this, after fusion-bonding and stretching the coupler body, it is possible to use the micro torch or the like that was subsequently used for fusion-stretching as it is to make the port a non-reflection end, It does not require special equipment and can be manufactured quickly and easily.

[Brief description of drawings]

1 and 2 are side views showing an example of a terminal of a port of an optical fiber calap according to the present invention, FIG. 3 is a perspective view showing an example of a fusion splicing type optical fiber calap, and FIG. 4 is an optical fiber calap. FIG. 3 is a schematic configuration diagram showing a wavelength multiplexing two-way optical communication system using the. 11 …… Port.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Suzuki 1440 Rokuzaki, Sakura-shi, Chiba Fujikura Electric Cable Co., Ltd. Sakura factory (56) References JP-A-61-284707 (JP, A)

Claims (1)

(57) [Claims] 1. A distributed-coupling type optical fiber coupler having two or more optical fibers spliced and fused and drawn, wherein at least one of the ports is heated and drawn to reduce its diameter. An optical fiber coupler characterized by being fused and made into a non-reflective end.